Poly-axial bone screw mating seat

ABSTRACT

Embodiments of bone securing system including a coupling element having a seat are described generally herein. Other embodiments may be described and claimed.

RELATED APPLICATIONS

This Application is a Non-Provisional of Provisional (35 USC 119(e))application 60/784,220 filed on Mar. 20, 2006, the entireties of whichare incorporated by reference herein.

TECHNICAL FIELD

The present invention relates generally to poly-axial bone screws and,more particularly, to poly-axial bone screws having improved grippingaction between a screw head and a coupling element seat of the bonescrew.

BACKGROUND ART

Bone securing systems may be provided to couple a bone stabilization rodor element to a bone securing member. In some systems a coupling membermay be provided between the bone stabilization rod an bone securingmember. The coupling member or element may include an interface betweena portion of the bone securing member and the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate perspective view of a poly-axial bonesecuring system before and after assembly of the components of thesystem, in accordance with one embodiment of the invention.

FIG. 1C illustrates a cross-sectional view of the poly-axial bonesecuring system of FIG. 1B.

FIG. 2A illustrates a perspective view of the coupling element, inaccordance with one embodiment of the invention.

FIG. 2B illustrates a cross-sectional side view of the coupling elementof FIG. 2A.

FIG. 2C illustrates a cross-sectional top view of the coupling elementof FIG. 2A.

FIG. 3B illustrates a cross-sectional top view of the coupling elementof FIG. 3A.

FIG. 4A illustrates a cross-sectional side view of the poly-axial bonesecuring system.

FIG. 4B illustrates a magnified view of the interface between the bonesecuring member head and a flexible J-shaped seat of the couplingelement of FIG. 4A.

DETAILED DESCRIPTION

FIG. 1A illustrates an exploded view of a poly-axial bone securingsystem 10, in accordance with an embodiment of the invention. Thepoly-axial bone securing system 10 includes a bone securing member 12,rod to bone securing member coupling element 22, saddle member 29, andmating cap 28. In an embodiment, the bone securing member 12 has athreaded shaft portion 14 (threads not shown), a head portion 16, a tip18, and a neck portion 20. The tip 18 may be configured to penetrate apatient's bone and be located at he distal end of the threaded shaftportion 14 opposite the bone securing member head 16. In an embodimentthe bone securing member 12 may be a pedicle screw.

A neck portion 20 may be located between the screw head 16 and thethreaded shaft 14. In one embodiment, the width of the neck portion 20is narrower than the width of the threaded shaft 14, to enable increasedpoly-axial motion of the coupling element 22 when engaged with the bonesecuring member head 16. The coupling element 22 includes an opening 24at a bottom surface configured to permit the bone securing tip 18 andthe threaded shaft 14 to pass through. In an embodiment, the bonesecuring member head 16 may have a curved underside. The head 16 curvedunderside may engage a coupling member 22 seat 30 (FIG. 1C). Thecoupling element 22 may includes a side groove or channel 26 formed bytwo arms 25A, 25B for receiving a bone stabilization rod 11 (FIG. 1B)therein.

The bone securing system 10 may further include a mating cap 28including a snap cap with set screw, interlocking cap, or a lock capwith set screw positioned therein. In an embodiment the mating cap 28may lock a rod 11 within the coupling element 22 groove 26 bytransferring a downward force from the rod 11, saddle member 29,securing member 12 head 16, and coupling element 22 seat 30. In anembodiment the saddle 29 may rest within the channel 26 on top of thebone securing member 12 head 16 and assist with holding the system 10together after installation. The saddle 29 may have a bottom surfaceconfigured to rest on securing member 12 head 16 top surface and a topsurface inwardly curved to matingly receive a cylindrical rod 11.

In an embodiment, the saddle 29 may act as an intermediate structure tofacilitate an even distribution of load forces onto the bone securingmember 12 head 16 top surface, the load forces created by the mating cap28 being tightened onto a rod 11. The coupling head 22 includes a seat30 to provide gripping and holding power between the coupling member 22and the bone securing member 12 head 16 to limit any post-installationshifting of the bone securing member 12 with respect to the couplingelement 22.

FIG. 1B illustrates a perspective view of an assembled poly-axial bonesecuring system of FIG. 1A. In an embodiment the bone securing member12, after insertion into the coupling element 22 via the opening 24 maybe driven into a bone (to be secured), such as a spinal pedicle viaknown techniques. The bone securing member 12 head 16 may include a Hex,Phillips, or other tool mating opening 32 (FIG. 1C). the securing member12 may driven into bone up to the shoulder 20 to permit poly-axialarticulation between the coupling member 22 and bone securing member 12head 16 prior to mating cap 28 lock down. A rod 11 may be inserted intothe channel 26 after the bone securing member 12 is installed in a bone.

The rod 11 and coupling element 22 may be adjusted into a desiredrelationship to the bone securing member 12 until the mating cap 28 islocked against the rod 11. FIG. 1C is a cross-sectional side view of thebone securing system 10 shown in FIG. 1B, taken along lines A-A. In anembodiment, the bone securing member head 16 underside may engage andrest upon a coupling element 12 seat 30. The seat 30 may define theopening 24 shape.

FIG. 2A is a perspective side view of the coupling element 22, inaccordance with an embodiment of the invention. FIG. 2B is across-sectional side view of the coupling element 22 of FIG. 2A, takenalong lines A-A and FIG. 2C is a cross-sectional top view of thecoupling element 22 of FIGS. 2A and 2B. The coupling element 22 includesa multi-faceted 31 seat 30 that provides a discrete number of contactsurfaces or points 34 for engaging the bone securing member 12 head 16underside.

The coupling element 22 may also include a lip 36 for engaging a flangeor protruding portion of the mating cap 28 to fixably couple the rod 11,coupling element 22, and bone securing member 12 together. As shown inFIG. 2C, the multi-faceted 31 seat 30 may be configured as a polygonincluding an octagon having eight distinct side surfaces or facets 31.When a bone securing member head 16 is seated within a multi-facetedseat 30 and pressed against the seat 30 via a mating cap 28 discretefrictional or gripping forces may be generated primarily at theinterface points 34 indicated by the dots near the center of each sideor facet 34 of the polygon-shaped seat 30.

The seat 30 may provide increased gripping forces between the bonesecuring member 12 head 16 and the coupling element 22 by providing adiscrete number of contact points. In an embodiment when a bone securingmember 12 head 16 is pressed into a seat 30, the primary contactsbetween the head 16 and the seat 30 are focused at or near the points34. The multi-faceted 31 seat 30 may provide improved gripping actionbetween the coupling element 22 and the bone securing member 12 head 16due to the discrete number of contacts 34, reaction load, and head 16deformation at the seat interface 30. The seat interface 30 may deformat each contact point 34 when a mating cap 38 is located into place dueto pressure or stress at points 34. In an embodiment the seat 30discrete contact points 34 may significantly increase the force per areabetween the coupling element 22 and securing member 12.

FIG. 3A is a perspective view of another coupling element 40 inaccordance with an embodiment of the invention. The coupling element 40includes a channel 42 for receiving a rod (not shown) therein and a seat44 having a discrete number of prongs 46. Each prong 46 may curveinwardly at a bottom portion of the coupling element 40. FIG. 3B is across-section top view of the coupling element 40. When a bone securingmember 12 head 16 is seated on and pressed against the seat 44, it mayengage the discrete number of prongs 46. In an embodiment the interiorsurface of the prongs 46 form the seat 44 and provide increasedfrictional force between the bone securing member 12 head 16 and theseat 44 in accordance with the principles discussed above with respectto coupling element 22.

The coupling element 40 may also provide increased flexibility and theability to dynamically distribute loads across the seating surface dueto the discrete number of prongs 46. The coupling element 40 maywithstand and handle external forces reliably and not shift relative tothe bone securing member 12 in the presence of external forces. Inaddition to prongs 46 may provide flexibility between the couplingelement 40 and bone securing member 12 head 16 so loads may bedistributed more evenly across the prongs 46.

FIG. 4A is a cross-sectional view of a bone securing system 50 inaccordance with an embodiment of the invention and FIG. 4B is anenlarged view of a section of the system 50. The bone securing system 50includes a bone securing member 52 having a threaded shaft 54, a neckportion 60, a tip 58, and a spherical-shaped screw head 56. In anembodiment, the neck portion 60 is narrower than the threaded shaft 54to allow increased poly-axial articulating motion between the couplingelement 62 and bone securing member 52. The coupling head 62 may includea U-shaped channel 64 for receiving a bone stabilization rod 11 therein.

The system 50 may include a mating cap 68 (such as a snap cap)configured to be received and locked within a correspondingly shapedchamber 66 of the coupling element 62. The chamber 66 may include aledge 70 configured to lock the mating cap 68 within the chamber 66. Asshown n FIG. 4B, the coupling element 62 may include a circular J-shapedseat 71 having a J-shaped lip 72. The J-shaped seat 71 may be configuredto flexibly hod the bone securing member 52 head 56 within the couplingelement 62. The J-shaped seating surface lip 72 may provide greaterability to withstand and distribute loads between the seating surface 71and the head 56, thus being less prone to shifting or breaking due toexternal forces. In an embodiment the seat 72 may be segmented into adiscrete number of J-shaped lips 72 similar to prongs 46 shown in FIG.3A.

The accompanying drawings that form a part hereof show, by way ofillustration and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein individually or collectively by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any single invention or inventive concept, if more thanone is in fact disclosed. Thus, although specific embodiments have beenillustrated and described herein, any arrangement calculated to achievethe same purpose may be substituted for the specific embodiments shown.This disclosure is intended to cover any and all adaptations orvariations of various embodiments. Combinations of the aboveembodiments, and other embodiments not specifically described herein,will be apparent to those of skill in the art upon reviewing the abovedescription.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In the foregoing Detailed Description,various features are grouped together in a single embodiment for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted to require more features than are expressly recited ineach claim. Rather, inventive subject matter may be found in less thanall features of a single disclosed embodiment. Thus the following claimsare hereby incorporated into the Detailed Description, with each claimstanding on its own as a separate embodiment.

1. A coupling element, the coupling element including a seat, the seat having an opening that a first portion of a bone securing member may pass through and the opening having a discrete number of non-contiguous contact elements, each contact element capable of engaging a second portion of the bone securing member.
 2. The coupling element of claim 1, the bone securing member first portion including a bone securing element.
 3. The coupling element of claim 1, the bone securing member second portion including an at least partially spherical head.
 4. The coupling element of claim 1, wherein at least one of the limited number of contact elements is deformable.
 5. The coupling element of claim 1, wherein at least one of the limited number of contact elements is flexible.
 6. The coupling element of claim 1, wherein each contact element has a contact point capable of engaging the bone securing element second portion.
 7. The coupling element of claim 1, wherein at least one of the limited number of contact elements includes a prong.
 8. The coupling element of claim 1, wherein the coupling element couples a bone securing member to a rod.
 9. The coupling element of claim 8, the coupling element further including a rod receiving channel.
 10. A system, including: a bone securing member; a rod; and a coupling element for coupling to a bone securing member to the rod, the coupling element including a seat, the seat having an opening that a first portion of the bone securing member may pass through and the opening having a limited number of contact elements, each contact element capable of engaging a second portion of the bone securing member.
 11. The system of claim 10, the bone securing member first portion including a bone securing element.
 12. The system of claim 10, the bone securing member second portion including an at least partially spherical head.
 13. The system of claim 10, wherein at least one of the limited number of contact elements is deformable.
 14. The system of claim 10, wherein at least one of the limited number of contact elements is flexible.
 15. The system of claim 10, wherein each contact element has a contact point capable of engaging the bone securing element second portion.
 16. The system of claim 10, wherein at least one of the limited number of contact elements includes a prong.
 17. The system of claim 10, the coupling element further including a rod receiving channel.
 18. A coupling element, the coupling element including a seat, the seat having an opening that a first portion of a bone securing member may pass through and the opening having a flexibly deformable contact element, the contact element capable of flexibly engaging a second portion of the bone securing member.
 19. The coupling element of claim 18, the bone securing member first portion including a bone securing element.
 20. The coupling element of claim 18, the bone securing member second portion including an at least partially spherical head.
 21. The coupling element of claim 18, wherein the flexibly deformable contact element includes a plurality of discrete sub-elements each sub-element capable of flexibly engaging a second portion of the bone securing member.
 22. The coupling element of claim 18, wherein the flexibly deformable contact element includes a flexibly deformable lip, the lip capable of flexibly engaging a second portion of the bone securing member.
 23. The coupling element of claim 18, wherein the coupling element couples a bone securing member to a rod.
 24. The coupling element of claim 23, the coupling element further including a rod receiving channel.
 25. A system, including: a bone securing member; a rod; and a coupling element for coupling to a bone securing member to the rod, the coupling element including a seat, the seat having an opening that a first portion of a bone securing member may pass through and the opening having a flexibly deformable contact element, the contact element capable of flexibly engaging a second portion of the bone securing member.
 26. The system of claim 25, the bone securing member first portion including a bone securing element.
 27. The system of claim 25, the bone securing member second portion including an at least partially spherical head.
 28. The system of claim 25, wherein the flexibly deformable contact element includes a plurality of discrete sub-elements each sub-element capable of flexibly engaging a second portion of the bone securing member.
 29. The system of claim 25, wherein the flexibly deformable contact element includes a flexibly deformable lip, the lip capable of flexibly engaging a second portion of the bone securing member. 